PSTN trunks (i.e., Public Switched Telephone Network communication line between two switching systems) are intranode communication links in a network. A trunk can connect any combination of Internet Packet Exchange (IPX), Internet Gateway Exchange (IGX) or other nodes. Trunks are activated after node configuration by a telco (i.e., local telephone company). PSTN protocol is responsible for path establishment, release and other call relating signaling. PSTN protocol may not be able to control the call procedures, but rather the PSTN protocol transfers information about the line state. The PSTN protocol has a relatively small functional part, which is concerned with path setup, release of the path, call collision resolution and handling of new calls. The PSTN basically connects point A to point B.
A defective PSTN trunk generates signaling errors during attempted call setup or call teardown. Other resources coupled to the setup or teardown process may also generate errors. For example, an internal resource such as a Digital Signal Processor (DSP) can generate signaling errors as well. These errors are tracked by a PSTN switch which, based on exceeding counter thresholds for a given period, may remove the resource or channel (e.g., PSTN trunk) from service. This is undesirable because the customer paying for use of this trunk from the switched network is not able to use this trunk as it is disabled by the network. This may result in lost revenue for the customer. In addition, the customer must often pay a service fee to have this trunk restored to service by the telco which provides this trunk, which results in unnecessary service or maintenance fees. A PSTN trunk may fail due to several reasons. Errors within the PSTN can originate from human error, acts of nature, hardware or software failure, or overloads. The majority of errors result from human error or hardware failure.
An effective PSTN trunk results from the effectiveness of the hunting algorithm used to determine the availability of open channels for use of channel related resources. Any one of the shared resources or entities within a system may develop problems that when allocated and used in the course of handling an incoming or outgoing call, may cause that call to fail. This call failure is recorded as accumulated and compared to the number of accumulated call successes and call attempts. The ratio of call successes to the call attempts is the call success rate. As the number of call failures increases the call success rate declines.
An additional problem due to defective resources, is that a defective resource such as a PSTN trunk or an internal DSP resource, would cause the call connect rate (i.e., percentage of successful calls) to be disproportionately skewed which would make the quality of the system appear to be far worse than it was.
The call success rate is an important metric when comparing Remote Access Server (RAS) products from different vendors. Lower call success rates imply greater lost calls and lost revenues to the customer. Even though a single instance of a resource may fail, this may interact with the switch's own trunk group hunting algorithm to exacerbate the accumulation of failed calls. A switch's channel hunting algorithm may “stop” at a particular channel, offering new calls that are immediately rejected by the RAS equipment only to be immediately offered another call (which will also be rejected) if that channel has an instance of a failed resource. This cycle of offered call, reject the call, and another offered call to the same channel can continue indefinitely. Even though there may be other channels available for use, the switches hunting algorithm must first move on beyond this faulty channel before they can be used. This situation then biases the offered calls toward a defective channel dramatically reducing the call success rate. Consequently, existing hunting algorithms do not focus on maximizing call connect rate, thus the call connect rate can be substantially worse. Moreover, existing hunting algorithms do not attempt to minimize the PSTN (switch) busying out channels.
It would be desirable to provide a method of selecting reliable resources and channels for use in order to provide stable service to customers. For example, a known substandard resource would not be desirable for use. In addition, it would also be desirable to provide a method of restoring resources and channels to service after the resources and channels have been removed from service.